Relay assignment schemes for multiple source-destination cooperative networks

In this paper, we consider cooperative networks comprising multiple simultaneous transmitting source-destination pairs. Specifically, we propose two relay assignment schemes whereby one relay is assigned to one pair at any given time. It is assumed that the number of relays equals or exceeds the number of pairs. This assumption is practical because in future wireless networks, any node in the network can serve as a relay. Both assignment schemes are based on the quality of the subchannels, implying that estimates of the subchannels should be available before the relays are assigned to the pairs. The first assignment scheme is optimal since it considers all possible relay assignment permutations. The second one is suboptimal since it considers only a subset of the possible permutations. The advantages of the latter is that it makes the performance analysis more tractable and reduces the complexity of the assignment process. We derive closed-form expressions for the end-to-end bit error rate performance and show that the full diversity is maintained in both schemes, which equals the number of relays (assuming no direct path between the source and destination nodes). We give several numerical examples that validate the theoretical results.